1. Technical Field
The present disclosure relates to methods and apparatus for detecting polarizing direction of electromagnetic waves and, particularly, to a carbon nanotube based method and apparatus for detecting polarizing direction of electromagnetic waves.
2. Description of Related Art
Polarizing direction is an important property of an electromagnetic wave. One method for detecting the polarizing direction of visible light includes disposing a polarizer and a target in the path of the visible light, and rotating the polarizer. The polarized visible light goes through the polarizer and irradiates the target. As the polarizer rotates, the light on the target changes periodically from dark to bright. When the light on the target is at its darkest, the polarizing direction of the visible light is perpendicular to the polarizing direction of the polarizer. When the light on the target is at its brightest, the polarizing direction of the visible light is parallel to the polarizing direction of the polarizer.
However, the above observational methods for determining the polarizing direction are not suitable for invisible light such as infrared, ultraviolet, and other wavelengths. In general, to detect the polarizing direction of invisible light, a photoelectric sensor is disposed at the target position. Thus, the invisible light is transformed to electric signals, and the electric signals can be measured.
However, the method for detecting the invisible light is complicated and requires many optical and electrical devices. In addition, the conventional polarizer can only achieve good polarization in certain regions of the electromagnetic spectra, (e.g. microwave, infrared, visible light, ultraviolet, etc.), and does not achieve uniform polarization over the entire spectrum. Thus, when the wavelength of the light changes, the polarizer has to be changed accordingly.
Carbon nanotubes (CNT) are a novel carbonaceous material having an extremely small size and an extremely large specific surface area. Carbon nanotubes have received a great deal of interest since the early 1990s, because they have interesting and potentially useful electrical and mechanical properties, and have been widely used in a plurality of fields. A disordered carbon nanotube film based apparatus for detecting electromagnetic waves is disclosed in “Bolometric infrared photoresponse of suspended single-walled carbon nanotube films,” Science, Mikhail E. Itkis et al, vol 312, P412 (2006). Carbon nanotubes have a uniform absorbability of electromagnetic waves having different wavelengths. When the disordered carbon nanotube film is irradiated by electromagnetic waves having different wavelengths, the resistance of the disordered carbon nanotube film changes. Thus, the intensity of the incident electromagnetic wave can be detected by detecting the resistance of the irradiated disordered carbon nanotube film.
However, the above apparatus can only detect the intensity of an electromagnetic wave, and not the polarizing direction thereof. Further, to detect the resistance, complicated additional apparatuses must be used.
What is needed, therefore, is to provide a simpler method and apparatus for detecting polarizing direction of an electromagnetic wave.